Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see
Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Prerequisites for Multilink Frame Relay FRF.16.1

Multilink Frame Relay must be configured on the peer device.

Restrictions for Multilink Frame Relay FRF.16.1

ISDN interfaces and any type of virtual interface cannot be a bundle link.

Information About Multilink Frame Relay FRF.16.1

Benefits of Multilink Frame Relay FRF.16.1

Flexible Pool of Bandwidth

By combining multiple physical interfaces into a bundle, you can design a Frame Relay interface that has more bandwidth than is available from any single physical interface. For example, many new network applications require more bandwidth than is available on a T1 line. One option is to invest in a T3 line; however, T3 lines can be expensive and are not available in some locations. Multilink Frame Relay provides a cost-effective solution to this problem by allowing multiple T1 lines to be aggregated into a single bundle of bandwidth.

Greater Service Resilience When Links Fail

Greater service resilience is provided when multiple physical interfaces are provisioned as a single bundle. When a link fails, the bundle continues to support the Frame Relay service by transmitting across the remaining bundle links.

Link Integrity Protocol Control Messages

For link management, each end of a bundle link follows the MFR Link Integrity Protocol and exchanges link-control messages with its peer (the other end of the bundle link). For a bundle link to be brought up, each end of the link must complete an exchange of ADD_LINK and ADD_LINK_ACK messages. To maintain the link, both ends periodically initiate the exchange of HELLO and HELLO_ACK messages. This exchange of hello messages and acknowledgments serves as a keepalive mechanism for the link. If a router is sending hello messages but not receiving acknowledgments, it will resend the hello message up to a configured maximum number of times. If the router exhausts the maximum number of retries, the bundle link line protocol is considered down (nonoperational).

The bundle link interface’s line protocol status is considered up (operational) when the peer device acknowledges that it will use the same link for the bundle. The line protocol remains up when the peer device acknowledges the hello messages from the local router.

The bundle interface’s line protocol status is considered up when the Frame Relay data-link layer at the local router and peer device is synchronized using the Local Management Interface (LMI), when LMI is enabled. The bundle line protocol remains up as long as the LMI keepalives are successful.

Class A (Single Link)

The Frame Relay bundle is provisioned when one or more bundle links indicate by issuing a BL_ACTIVATE message that operational bandwidth is available. When this occurs, the bundle emulates a physical link by issuing a PH_ACTIVATE message to the data-link layer.

When the operational bandwidth of a bundle link fails to meet operational requirements (for instance, if it is in rollback mode), the bundle link issues a BL_DEACTIVATE message. When all bundle links are down in a class A bundle, a PH_DEACTIVATE message is sent to the data-link layer, indicating that the Frame Relay bundle cannot accept frames.

Class B (All Links)

The Frame Relay bundle is provisioned when all bundle links indicate by issuing a BL_ACTIVATE message that operational bandwidth is available. When this occurs, the bundle emulates a physical link by issuing a PH_ACTIVATE message to the data-link layer.

When the operational bandwidth of a bundle link fails to meet operational requirements (for instance, if it is in loopback mode), the bundle link issues a BL_DEACTIVATE message. When any bundle link is down in a class B bundle, a PH_DEACTIVATE message is sent to the data-link layer, indicating that the Frame Relay bundle cannot accept frames.

Class C (Threshold)

The Frame Relay bundle is provisioned when the minimum number of links in the configured bundle issue a BL_ACTIVATE message. When this occurs, the bundle emulates a physical link by issuing a PH_ACTIVATE message to the data-link layer.

When the number of bundle links that are issuing a BL_ACTIVATE message falls below the configured threshold value, a PH_DEACTIVATE message is sent to the data-link layer, indicating that the Frame Relay bundle cannot accept frames.

Load Balancing with Multilink Frame Relay FRF.16.1

Multilink Frame Relay provides load balancing across the bundle links within a bundle. If a bundle link chosen for transmission happens to be busy transmitting a long packet, the load-balancing mechanism can try another link, thus solving the problems seen when delay-sensitive packets have to wait.

How to Enable Multilink Frame Relay FRF.16.1

Configuring a Multilink Frame Relay Bundle

To configure the bundle interface for multilink Frame Relay, perform the steps in this section.

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacemfrinterface-number

4.Do one of the following:

frame-relaymultilinkbandwidth-class [a | b | c [threshold]]

5.frame-relayintf-typedce

6.frame-relaymultilinkbidname

7.frame-relaymultilinkoutput-thresholdbytes

8.interfacemfrinterface-number.subinterface-numberpoint-to-point

9.ipaddressip-addressmask

10.frame-relayinterface-dlcidlci

11.end

12.showframe-relaymultilink

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interfacemfrinterface-number

Example:

Router(config)# interface mfr mfr1

Configures a multilink Frame Relay bundle interface.

Step 4

Do one of the following:

frame-relaymultilinkbandwidth-class [a | b | c [threshold]]

Example:

Router(config-if)# frame-relay multilink bandwidth-class a

Example:

Example:

Example:

Router(config-if)# frame-relay multilink bandwidth-class b

Example:

Example:

Example:

Router(config-if)# frame-relay multilink bandwidth-class c 3

(Optional) Specifies the bandwidth class criterion used to activate or deactivate a Frame Relay bundle.

Class A (single link)--The bundle will activate when any bundle link is up and will deactivate when all bundle links are down (default).

Class B (all links)--The bundle will activate when all bundle links are up and will deactivate when any bundle link is down.

Class C (threshold)--The bundle will activate when the minimum configured number of bundle links is up (the threshold) and will deactivate when the minimum number of configured bundle links fails to meet the threshold.

Note

If no bandwidth class criterion is specified by using the frame-relaymultilinkbandwidth-classcommand, the Frame Relay bundle will default to class A (single link).

Step 5

frame-relayintf-typedce

Example:

Router(config-if)# frame-relay intf-type dce

Configures a device to function as the data circuit-terminating equipment (DCE).

Only one end of a link should be configured as the DCE. The other end will function as the data terminal equipment (DTE), which is the default setting.

This command can be used only if Frame Relay switching has been enabled by entering theframe-relayswitching command in global configuration mode.

Step 6

frame-relaymultilinkbidname

Example:

Router(config-if)# frame-relay multilink bid router1

(Optional) Assigns a bundle identification name to a multilink Frame Relay bundle.

The bundle identification (BID) will not go into effect until the interface has gone from the "down" state to the "up" state. One way to bring the interface down and back up again is by using theshutdown and noshutdown commands in interface configuration mode.

Step 7

frame-relaymultilinkoutput-thresholdbytes

Example:

Router(config-if)# frame-relay multilink output-threshold 500

(Optional) Configures the number of bytes that a bundle link will transmit before the load-balancing mechanism causes transmission to roll over to the next available link.

When configured on the bundle interface, this command applies to all bundle links in the bundle.

The bundle link identification (LID) will not go into effect until the interface has gone from the "down" state to the "up" state. One way to bring the interface down and back up again is by using the shutdown and noshutdown commands in interface configuration mode.

Step 7

frame-relaymultilinkhelloseconds

Example:

Router(config-if)# frame-relay multilink hello 9

(Optional) Configures the interval at which a bundle link will send out hello messages.

The default value is 10 seconds.

Step 8

frame-relaymultilinkackseconds

Example:

Router(config-if)# frame-relay multilink ack 6

(Optional) Configures the number of seconds that a bundle link will wait for a hello message acknowledgment before resending the hello message.

The default value is 4 seconds.

Step 9

frame-relaymultilinkretrynumber

Example:

Router(config-if)# frame-relay multilink retry 3

(Optional) Configures the maximum number of times that a bundle link will resend a hello message while waiting for an acknowledgment.

The default value is 2 tries.

Step 10

end

Example:

Router(config-if)# end

Ends the configuration session and returns to privileged EXEC mode.

Step 11

showframe-relaymultilink

Example:

Router# show frame-relay multilink

(Optional) Displays the current Frame Relay multilink configuration.

Monitoring and Maintaining Multilink Frame Relay FRF.16.1

To monitor and maintain multilink Frame Relay, perform the steps in this section.

The following examples show output for the
showframe-relaymultilink command when the
serialnumber keyword and argument and the
detailed option are specified. Detailed information about the specified bundle links is displayed. The first example shows a bundle link in the "idle" state. The second example shows a bundle link in the "up" state:

RFCs

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Feature Information for Multilink Frame Relay FRF.16.1

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

The following commands were introduced or modified:
debugframe-relaymultilink,encapsulationframe-relaymfr,frame-relaymultilinkack,frame-relaymultilinkbandwidth-class,frame-relaymultilinkbid,frame-relaymultilinkhello,frame-relaymultilinklid,frame-relaymultilinkoutput-threshold,frame-relaymultilinkretry,interfacemfr,showframe-relaymultilink.

Frame Relay fragmentation (FRF.12)

12.3(9) 12.3(11)T 12.2(30)S

Frame Relay Fragmentation based upon FRF.12 allow long data frames to be fragmented into smaller pieces and interleaved with real-time voice frames or other delay-sensitive traffic.

In 12.3(9), this feature was introduced.

Multilink Frame Relay (FRF.16.1) - Variable Bandwidth Class

12.0(30)S 12.4(2)T 15.0(1)S

Multilink Frame Relay (FRF.16.1) variable bandwidth class support allows you to specify the criterion used to activate or deactivate a Frame Relay bundle.

In 12.0(30)S, this feature was introduced.

Glossary

BID--Bundle identification. The BID is the name used to identify the bundle. The BID can be assigned, or the default can be used.

BL_ACTIVATE--A message that controls the addition of a bundle link to a Frame Relay bundle.

BL_DEACTIVATE--A message that controls the removal a bundle link from a Frame Relay bundle.

bundle--A logical grouping of one or more physical interfaces using the formats and procedures of multilink Frame Relay. A bundle emulates a physical interface to the Frame Relay data-link layer. The bundle is also referred to as the MFR interface
.

bundlelink--An individual physical interface that is a member of a bundle.

HELLOmessage--A message that notifies a peer endpoint that the local endpoint is in the operational state (up).

HELLO_ACK--A message that notifies a peer endpoint that a hello message has been received.

LID--link identification. The LID is the name used to identify a bundle link. The LID can be assigned, or the default can be used.

LMI--Local Management Interface. A set of enhancements to the basic Frame Relay specification. LMI includes support for a keepalive mechanism, which verifies that data is flowing; a multicast mechanism, which provides the network server with its local DLCI and the multicast DLCI; global addressing, which gives DLCIs global rather than local significance in Frame Relay networks; and a status mechanism, which provides an ongoing status report on the DLCIs known to the switch.

NNI--Network-to-Network Interface. The interface between two Frame Relay devices that are both located in a private network or both located in a public network.

PH_ACTIVATE--A message that indicates that the Frame Relay bundle is up.

PH_DEACTIVATE--A message that indicates that the Frame Relay bundle is down.

UNI--User-to-Network Interface. The interface between a Frame Relay device in a public network and a Frame Relay device in a private network.